Synthesis of Furo[3,2-h]isoquinolines Based on the Nenitzescu Reaction

The interaction of derivatives of isoquinolino-5,8-quinone with various enaminocarbonyl compounds occurred regioselectively to give substituted furo[3,2-h]quinolines.     

Synthesis of Furoindoles and Benzodifurans by the Nenitzescu Reaction

New derivatives of furoindole and benzodifuran were synthesized by the condensation of 3-methyl-4,5-dioxobenzofuran with enamines under the conditions of the Nenitzescu reaction.     

Fluorescent Pyranoindole Congeners: Synthesis and Photophysical Properties of Pyrano[3,2-f], [2,3-g], [2,3-f], and [2,3-e]Indoles

This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2-f]indole, pyrano[2,3-g]indole, pyrano[2,3-f]indole, and pyrano[2,3-e]indole and photophysical studies in this series. The synthesis of pyrano[3,2-f], [2,3-g], and [2,3-e]indoles involve a tandem of Bischler–Möhlau reaction of 3-aminophenol with benzoin to form 6-hydroxy- or 4-hydroxyindole followed by Pechmann condensation of these hydroxyindoles with β-ketoesters. Pyrano[2,3-f]indoles were synthesized through the Nenitzescu reaction of p-benzoquinone and ethyl aminocrotonates and subsequent Pechmann condensation of the obtained 5-hydroxyindole derivatives. Among the pyranoindoles studied, the most promising were pyrano[3,2-f] and [2,3-g]indoles. These compounds were characterized by moderate to high quantum yields (30–89%) and a large (9000–15,000 cm⁻¹) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2-f] and [2,3-g]indoles to demonstrate their positive solvatochromism, and the data collected was analyzed using Lippert-Mataga equation. Quantum chemical calculations were performed to deepen the knowledge of the absorption and emission properties of pyrano[3,2-f] and [2,3-g]indoles as well as to explain their unusual geometries and electronic structures.     

Dialkyl quinone-2,3-dicarboxylates in the Nenitzescu reaction

Diethyl naphthoquinone-2,3-dicarboxylate reacts with different enamines to give 5-oxo-1,5-dihydro-benzo[g]indole-3,4,9b-tricarboxylate derivatives by migration of one ethoxycarbonyl group. These new products aromatize to planar indoles by elimination of one ethoxycarbonylgroup. With an N,N-dimethyl-enamine cyclization yields a 5-oxo-4,5-dihydro-cyclopenta[a]naphthalene-3,3a,4-tricarboxylate as well as a naphthyl-malonic acid derivative by migration of an ethoxycarbonylgroup.     

Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

Synthesis of thieno[2,3-e]-1,2,4-triazines

3-Methylmercapto-5-oxo-6-vinyl- and 2-methyl-3-mercapto-5-oxo-6-vinyl-2,5-dihydro-1,2,4-triazines were readily converted into the corresponding thieno[2,3-e]-1,2,4-triazine in one step by the action of phosphorus pentasulfide in pyridine. 4-Methyl-3-mercapto-5-oxo-4,5-dihydro-1,2,4-triazine is only converted into the 5-thioxo analog and no thiophene ring product was obtained under the same conditions. Thieno[2,3-e]-1,2,4-triazines were also more efficiently obtained by the action of phosphorus petnasulfide in pyridine on the appropriate 6-acylmethyl-3-mercapto-5-oxo-2,5-dihydro-1,2,4-triazine.     

Quinoneimines in the Nenitzescu reaction

The Nenitzescu reaction involving quinoneimines was studied; new 5-aminoindole, 5-aminobenzofuran, and 9-aminochromenopyridine derivatives were synthesized. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1640–1649, July, 2005.     

Synthesis of Furo[2,3-c]isoquinoline Derivatives

2-Methylfuro [2,3-c] isoquinolin-5(4H)one (X) and 1-phenylfuro[2,3-c] isoquinolin-5(4H)one (XI) were prepared from thermal cyelization via the Curtius rearrangement of 5-methyl-3-phenyl-2-furoyl azide (VI) and 3,4-diphenyl-2-furoyl azide (VII), respectively. Stability against acid, alkylation and conversion of the NHCO group to a C=N double bond of X and XI, which were synthesized, are described. Also, 5-substituted furo[2,3-c] isoquinolines (XVIIIa-c) and (XIXa-c) were prepared.     

Synthesis of New Furo[2,3-b]pyridine and Furo[3,2-d]pyrimidine Derivatives

Russian Journal of Organic Chemistry - New furo[2,3-b]pyridine and pyrido[3′,2′:4,5]furo[3,2-d]pyrimidine derivatives were synthesized from ethyl...     

Synthesis of 2H-benzo[g]furo/thieno/pyrrolo[2,3-e]indazoles via Intramolecular Dehydrogenation Photocyclization

A catalyst-,acid-and base-free,environmental-friendly method for synthesis of 2H-benzo[g]furo[2,3-e]indazoles,2H-benzo[g]-thieno[2,3-e]indazoles and 2H-benzo[g]...     

Synthesis and Ring Transformation of Pyrrolo[2,3-d][1,3]oxazine to Pyrrolo[2,3-d]Pyrimidines

A convenient route is reported for the synthesis of fused pyrrolo[2,3-d][1,3]oxazine and pyrrolo[2,3-d]-pyrimidine derivatives from 2-amino-1-benzyl-3-t-butoxycarbonyl]-4,5-dimethylpyrrole.     

Synthesis of furo[2,3-f]- and furo[3,2-e]indole derivatives

Two compounds — the diethylamides of 1,2-dimethyl-3-carbethoxy-6-carboxyfuro[2,3-f]- and 1,2-dimethyl-3-carbethoxy-5-carboxvfuro[3,2-e]indoles — are formed in the reaction of 1,2-dimethyl-3-carbethoxy-5-hydroxyacetic acid (I) with dimethylformamide and phosphorus oxychloride as a result of subsequent intramolecular cyclization of the intermediates. This constitutes evidence for formylation of the starting acid in the 6 and 4 positions. Formylation of the ethyl ester of acid I gives only the 6-formyl derivative, the intramolecular cyclization of which under the influence of sodium ethoxide gives 1,2-dimethyl-3,6-dicarbethoxyfuro[2,3-f]-indole. Hydrolysis of the latter with alcoholic alkali gives the corresponding dicarboxylic acid. The structures of the synthesized compounds were confirmed by the PMR, IR, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 766–769, June, 1977.     

Synthesis of 1H-pyrazino[1,2-a]pyrido[2,3-e]pyrazine and 2H-Pyrano[2,3-b]pyrido[2,3-e]pyrazine Derivatives

With a continuing interest on heteropolycyclic structures which may show biological activities, we synthesized new tricyclic derivatives in which the pyridopyrazine skeleton is fused with pyrazine 7 and 8, B , n = 1. However, the initial design of obtaining also the cyclohomologous structure B (n = 2) produced instead a pyranopyridopyrazine derivative 11 . Thus during the attempt to prepare a pyridodiazepine intermediate, beside a very small amount of the desired product 10 , the pyridopyrazine 9 was obtained. The latter compound reacted with chloroacetyl chloride/chloroketene to give 4-carbethoxy-10-(chloroacetyl)-5,10-dihydro-5-methyl-2H-pyrano[2,3-b]pyrido[2,3-e]pyrazin-2-one ( 11 ). In studying the behavior of this derivative, compounds 12–14 were obtained. Compounds 4b,c, 5a,b, 7, 8, 9 and 14 have been submitted to preliminary pharmacological screening as CNS depressant agents.     

Heterocyclic Quinones in the Nenitzescu Reaction. Synthesis of Furo- and Pyrrolobenzothiazoles from 2-Methyl-4,7-dioxobenzothiazole

Treatment of the enamines of acetylacetone and benzoylacetone with 2-methyl-4,7-dioxobenzothiazole under Nenitzescu reaction conditions gave furo[2,3-e]benzothiazoles (in acetic acid) and pyrrolo[2,3-e]benzothiazoles (in nitromethane). Using enamines of acetoacetic ester gave exclusively pyrrolo[2,3-e]benzothiazoles.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 252–258, February, 2005.     

Efficient One-pot Synthesis of Pyrrolo[2,1-a]isoquinoline and Pyrrolo[1,2-a]quinoline Derivatives

A one-pot sequential reaction for efficient synthesis of pyrrolo[2,1-a]isoquinoline and pyrrolo[1,2-a]-quinoline derivatives has been developed. The reaction included firstly the Cu-catalyzed three-component reaction of isoquinoline(quinoline), acetylenedicarboxylate and alkynylbenzene and then Cs₂CO₃-promoted intramolecular cyclization reaction of initially formed 1-alkenyl-2-alkynyl-1,2-dihydroisoquinoline(1,2-dihydroquinoline).     

Synthesis and Reaction of Some Indenopyridine and Thieno[2,3-b]Indeno[2,1-e]Pyridine Derivatives

Synthesis of indenopyridine-2-thione derivatives 6a-e via reaction of compound 1 with thioamides 2a-e in good yields. Several thieno[2,3-b]indeno[2,1-e]pyridine 9a-e have been synthesized. Some of them was used as a key intermediate in synthesis of 10-12. On the other hand, compound 1 reacted with various reagents to yield 16, 19, 21-24.     

Pyrrolo[1,2-a]thiéno[2,3-e]pyrazine. Etude chimique de la dihydro-4,5 oxo-5 pyrrolo[1,2-a]thiéno[2,3-e]pyrazine

The 4,5-dihydropyrrolo[1,2-e]pyrazin-5-one (1) exhibits lactam-lactim tautomerism. N-Electrophilic substitutions could be achieved via the intermediate of the substitutions could be achieved via the intermediate of the sodium salt la. The 5-chloropyrazine 11 obtained by chlorodehydroxylation of pyrazinone 1 allowed nucleophilic substitution. Thionation of the pyrazinone 1 afforded the thioxopyrazine 27 wich gave studied and the tautomerism of the hydrazinopyrazine 14 and its derivatives are discussed in terms of hydrazone and azine structures     

Pyrrolo[2,3-d] pyrimidines. I. 5-hydroxypyrrolo[2,3-d] pyrimidines

5-Hydroxy-7-alkyl-2-phenyl-7H-pyrrolo[2,3-d]pyrimidine-6-carbonitriles (VIIb-d) and 5-hydroxy-2-phenyl-7H-pyrrolo[2,3-d]pyrimidine-6-carboxylic acid, ethyl ester (VIIa) were prepared from 5-carbethoxy-4-chloro-2-phenylpyrimidine (IV) via 4-[(cyanomethyl)alkylamino[-2-phenyl-5-pyrimidinecarboxylic acid, ethyl esters (Vb-d) and 4-[(carboxymethyl)amino]-2-phenyl-5-pyrimidinecarboxylic acid, diethyl ester (Va), respectively. The hydroxy group of the pyrrolo-[2,3-d]pyrimidines could be methylated, acetylated and tosylated. Hydrolysis of 5-methoxy-7-methyl-2-phenyl-7H-pyrrolo[2,3-d]pyrimidine-6-carbonitrile (IX) afforded the corresponding amide (X).     

Synthesis and spectral data of pyrido[2,3-e]-as-triazines

The pyrido[2,3-e]-as-triazine and its 3-phenyl derivatives were prepared via cyclisation with polyphosphoric acid of suitable 3-substituted 2-aminopyridines obtained by reduction of the corresponding 2-nitropyridines. The 3-substituted 2-nitropyridines were obtained by action of hydrazine or benzoylhydrazide with the appropriate 3-halo-2-nitropyridines; only 3-fluoro-2-nitropyridine leads to the 3-substituted 2-nitropyridines. This experimental results are in agreements with the CNDO and MNDO calculations.     

Synthesis of perfluoroalkyl-substituted 4,5-dihydro-3H-pyrazolo[4,3-a]phenazines and tetrahydroimidazo[4,5-e]indazoles

Oxidation of 1-aryl-3-perfluoroalkyl-6,7-dihydro-1H-indazol-4(5H)-ones with selenium dioxide in the presence of sulfuric acid in glacial acetic acid, followed by treatment of 6,7-dihydro-1H-indazole-4,5-diones thus obtained with an equimolar amount of o-phenylenediamine in ethanol or with a mixture of 4-fluorobenzaldehyde and ammonium acetate in acetic acid, gave 3-aryl-1-perfluoroalkyl-4,5-dihydro-3H-pyrazolo-[4,3-a]phenazines and 6-aryl-2-(4-fluorophenyl)-8-perfluoroalkyl-1(3),4,5,6-tetrahydroimidazo[4,5-e]indazoles, respectively.